THE LOWER LIAS OF KEYNSHAM. 
23 
In all three districts a series of beds rich in semicostate 
ammonites, overlies beds containing large bisulcate ammo- 
nites, and is capped by strata containing abundant brevicone 
belemnites. 
The diagram shows the change in thickness and litho- 
logical character of the zones of the Lower Lias as we proceed 
from Sodbury on the north, through the Keynsham district, 
to the Radstock area further south. 
We have selected the Timsbury section as being the 
nearest exposure to the Keynsham area, which exhibits the 
characters which are peculiar to the Radstock Lias. The 
diagram needs no further explanation. 
DETAILED ACCOUNT OF THE KEYNSHAM LIAS. 
I. The sequence North of Keynsham (as shown in ex- 
posures 1, 2, 3, 4, 5). 
At the base, hard limestone beds are succeeded by a thick 
clay which always forms a very marked feature wherever 
the quarries have been worked low enough. In these hard 
beds we have found no ammonites, and those fossils that do 
occur abundantly ( Wald, perforata^ large Limas and species 
of Astarte and Cardlnia) cannot be considered to be of great 
value in fixing the horizon. Nevertheless, from the abund- 
ance of echinid remains in the thick clay immediately above, 
we are inclined to regard these hard beds as belonging to 
the Johnstoni division of the Psilonotus zone (compare 
Kelston station section and the section near Redland). 
The thick clay itself forms a very characteristic palaeonto- 
logical horizon, but it is very difficult and, as we think, 
very unimportant to say whether it should be grouped with 
the Angulatus beds above or with the Psilonotus beds 
below. Only one specimen of an ammonite has been found 
in it, and that, a very poor cast, showed tall, curved ribs, 
much after the angulatus pattern, but more spaced than 
